The present invention is generally related to microchip fabrication. More particularly, the invention relates to process controls and equipment related to certain chamber dependant fabrication steps.
In microchip fabrication, processing chambers are used in accomplishing various fabrication steps performed on a wafer. For example, among the numerous variety of steps are the non-exhaustive examples of annealing, cleaning, chemical vapor deposition, oxidation, and nitridation.
Chambers generally comprise a substantially planar and horizontal pedestal upon which the wafer rests during the processing within the chamber. The pedestal may also be known as a platen, stage or susceptor. A lift mechanism comprising pins which breach the pedestal from underneath provides a controlled disengagement from, and engagement of the wafer to, the pedestal surface. Wafers are transferred into and out of the chamber, and onto and off of the lift mechanism pins, by way of a robotic mechanism including a robot blade or fork at the end of a robotic arm.
Retention of the wafer to the pedestal while in the chamber may be accomplished mechanically by an edge ring. Alternatively, retention of the wafer to the pedestal while in the chamber may be accomplished electrostatically by an electrostatic chuck.
Wafers tend to be relatively brittle and susceptible to damage anytime one is handled or manipulated. For example, during a loading sequence into the chamber, contact of the pins with the wafer may be undesirably harsh thus damaging the wafer as transfer from the robot blade to the pins is accomplished. A wafer may also become mispositioned with respect to the pins when engagement therewith is undesirably harsh. A wafer mispositioned with respect to the pins will also be mispositioned when it is brought into contact with the pedestal. Likewise, contact of the wafer with the pedestal may also be undesirably harsh thus damaging the wafer as transfer from the pins to the pedestal is accomplished. With mechanical edge ring retention, damage to the wafer may result from excessive clamping forces. Similarly, damage may occur to the wafer upon the unloading of the wafer from the chamber. Late release of a mechanical edge ring or residual charge in an electrostatic chucking mechanism may result in damaged wafers if the pins attempt to separate the wafer from the pedestal prior to its complete release therefrom. If the retention force is great enough the wafer may break before release. The wafer may also break if it releases with a spring action and bounces. A wafer may also become mispositioned with respect to the pins during such a release. Apart from late or incomplete release of the wafer from the pedestal, contact of the pins with the wafer may be undesirably harsh during unimpeded separation of the wafer from the pedestal thus damaging the wafer. A wafer may also become mispositioned with respect to the pins during such a harsh contacting. Pin travel during separation of the wafer from the pedestal in preparation for transfer to the robot blade may reach the travel limit undesirably abruptly resulting in breakage of the wafer or mispositioning upon the pins as the wafer bounces upon the pins. Mispositioning upon the pins may result in mispositioning upon the robot blade which may in turn result in damage of the wafer as it is removed from the chamber through the access slot or thereafter in a subsequent transfer from the robot blade. Mispositioning upon the pins wherein the wafer is partially supported by the pins and the pedestal might also result in damage or breakage of the wafer when the robot blade enters the chamber to retrieve the wafer.
An operator may never be alerted to the various situations outlined above in a conventionally automated process resulting in wasteful utilization of chamber processing time on a broken or damaged wafer or on a wafer that is mispositioned on the pedestal. A wafer broken upon its loading into the chamber would desirably not be processed. Unbroken but mispositioned wafers may be subject to much lower yields due to edge effects, for example, in a sputtering process that could be avoided if the wafer were removed from the chamber and properly loaded. A wafer that is broken into several pieces, whether broken pre or post chamber processing, might not be removed from the chamber at all thus resulting in wafer debris within the chamber during further attempted wafer processing.
Therefore from the above, it is apparent that the need exists for detection of conditions within the chamber indicative of broken or out of position wafers. Such detection is advantageous at various points in the chamber processing. Of particular benefit is such detection subsequent to wafer transfer into the chamber but prior to chamber processing, and such detection subsequent to chamber processing but prior to wafer transfer out of the chamber.
Therefore, it is one object of the present invention to detect broken or out of position wafers within a processing chamber.
It is a further object of the present invention to provide such detection capabilities prior to and subsequent to wafer processing within the chamber.
In accordance with these and other objects of the invention, a microchip fabrication apparatus for processing a wafer comprises a chamber for processing the wafer, a plurality of lift mechanism pins within the chamber for supporting the wafer, and a plurality of sensors associated with said pins for detecting the wafer position.
Preferably, sensing is accomplished by capacitive means. Alternative sensing means associated with the lift mechanism pins, such as optical sensing, is envisioned.
A method of detecting an out of position wafer in a microchip fabrication chamber including a pedestal adapted for retention of a wafer thereto and a plurality of lift mechanism pins adapted to effect wafer to pedestal disengagement and engagement comprises the steps of providing wafer sensing means associated with at least one of said plurality of lift mechanism pins, and during a period when the lift mechanism pins are in a wafer disengaged position relative to the pedestal, sensing the presence of the wafer with respect to the at least one of the plurality of lift mechanism pins having the wafer sensing means.